THURSDAY, Dec. 11, 2008 (HealthDay News) -- Most deaths on Mount Everest occur during descents from the summit in the so-called "death zone" above 8,000 meters, and high-altitude cerebral edema appears to be associated with an increased risk of death.
That's the conclusion of researchers who analyzed the reported 212 deaths on the 29,000-foot mountain between 1921 and 2006.
The American, British and Canadian researchers found that the overall death rate for climbers and sherpas (locals hired to assist climbers) over those 86 years was 1.3 percent (1.6 percent among climbers and 1.1 percent among sherpas). Over the past 25 years, the death rate for climbers descending via the longer Tibetan northeast ridge was 3.4 percent, and 2.5 percent on the shorter Nepal route.
Excessive fatigue, a tendency to fall behind other climbers, and arriving at the summit later in the day were the factors most associated with risk of death, the study found. Many of those who died had symptoms such as confusion, a loss of physical coordination, and unconsciousness, all of which suggest high-altitude cerebral edema, a swelling of the brain caused by leakage of cerebral blood vessels.
Symptoms of high-altitude pulmonary edema (excessive fluid in the lungs) were rare among those who died on Everest. This surprised the researchers because high-altitude pulmonary edema is involved in most high-altitude-related deaths.
"We were also surprised at how few people died due to avalanches and ice falls in recent years... and that during descents, the mortality rate for climbers was six times that of sherpas," study leader Dr. Paul Firth, with the Massachusetts General Hospital department of anesthesia, said in a hospital news release.
The fact that fewer sherpas died during descents suggests that taking the time to acclimatize to high altitudes could improve climber survival. However, other factors may also be important, the study authors said.
"Most of the sherpas are born and live their lives at high altitudes, and the competitive process for expedition employment probably selects those who are best adapted to and most skilled for the work. So the ability of lowlanders to acclimate to these very high altitudes needs further investigation," Firth said.
The study was published Dec. 9 online issue of theBMJ.
The MedlinePlus Medical Encyclopedia has more about acute altitude sickness.